Martin, I don't know of anything that can be sprayed on to repel deer that you would not have to re apply after each rain and perhaps every so often. It might get more labor intensive then you want.
One thing I do in my woods is to lay branches over the sang patch where I can. Deer are kind of like water, in that, they will take \"the path of least resistance\" when browsing. If there is adequate browse outside and away from the branches they will not want to stick their faces into the branches to get to the sang. This would only need done as needed and probably only on patches where the deer travel through regularily. It does seem to help mine. I hope this helps.